Two distinct cloned segments of the African green monkey (Cercopithecus aethiops) genome that contain DNA sequences homologous to the control region of simian virus 40 are being studied. The primary sequence of the homologous regions was determined. When included in vectors constructed by molecular cloning these sequences provide transcriptional start sites, as measured by expression of an E. coli gene in the vector. However the monkey segments do not provide the "enhancer" function that is present in the SV40 control region. Thus, in order for transcription to start within the monkey sequences, an enhancer segment must be separately incorporated into the vector. The monkey DNA sequences hybridize with cellular RNA indicating that they are normally transcribed. One of the sequences, which is 450 base pairs in length, is embedded in a genomic DNA region that is especially rich in interspersed repeated sequences and is hypersensitive to DNase I in monkey chromatin.